Method of making waterproof sandpaper



June 23,' 1942. B. J. OAKES METHOD OF MAKING WATERPROOF SANDPAPER Original Filed March 10, 1933 Patented June 23, 1942 ME'rnonor MAKING WATERPROOF sANnrAPEa Byron J. Oakes, St. Paul, Minn., assgnor to Minnesota. Mining & Manufacturing Company, St. Paul, Minn., a corporation of Delaware Application March 10, 1933, Serial No. 660,318

` Renewed March 1, 1940 7 claims.

This invention relates, in general, to the preparation of abrasive articles, preferably in sheet form, and more particularly to the treatment of sheet material for obtaining or forming composite structures in the form of abrasives, such as far example that which is commonly known as sandpaper. Composite structures of the abrasive type, such as sandpaper or emergy cloth comprise generally--V (a) A base or backing .of sheet material which may bev felted, such as in the case of paper, or woven material, as in the case of cloth;

(b) A more of less nely comminuted resistant material having abrading properties, such as garnet, corundum, pulverized glass, and generally,

. natural and artificial abrasive materials; and

(c) A binder, generally in the form of an adhesive material, which serves to bind the abrasive to the base.

Where I have attempted to make abrasive products suitable for liquid sanding operations and having a high order of flexibility, in which the binding ingredients for the abrasive particles include the water repellant properties of materials of the generalA resinous type or resinvarnish type, including waterproofing materials such as oils, and utilize these materials in connection with the abrasive and the backing material to obtain an abrasive article having uniform properties of exibility, thickness in connection with a predetermined size of the grit of abrasive-particles, and abrasion resistance during operation for the life of the abrasive article, the application of the binder and the abrasive particles to a backing material such as paper, involves a number of perplexing problems due to the characteristics of the binding material, and the abrasive to react and make intimate contact with the binder; the nature of the reaction of the binder material or waterproong ingredients in connection with the` paper, ,the relative adjustment of the quantity of binder to the particles of grit or abrasive, to give abrading characteristics without clogging, all of which aiect the uniformity of the product, the life ofthe abrasive article as to its abrasive characteristics, flexibility and resistance to the liquids used in abrading operations, such as water, solutions of detergents and organic solvents, such as kerosene, gasoline and'oil.

'While the problems above enumerated, when giving consideration to the materials entering into making the composite comprising sandpaper, by reason of the characteristics of the backing material, usually comprising paper or cloth,

extremely vital, and the success or failure of the industry engaged in the production of waterproof sandpaper depends upon its ability to obtain all the benefits above enumerated with certainty, uniformity and economy.

It is therefore anl object of my invention to provide a waterproof sandpaper which includes the production of vsuchmaterial in which the characteristics of Waterproofness, resistance to decomposition by liquids used in abrading operations, with uniformity of product as to maximum abrading efficiency and with prolonged abrasive life, coupled with flexibility, may be economically practiced and with certainty of results.

It is also an object of my invention to provide an improved process of manufacturing sandpaper and the like abrasive articles in which the backing is conducted through the various steps of application of sizing adhesive, binder adhesive and grit in such manner that, subsequent to the application of grits to the adhesive and while the sheet `or backing having the grit thereon is passed through drying and heat-treating steps, the grit coated side of the sheet is maintained free of external mechanical pressure so as to prevent dulling of the sheet and thus produce an article in which the sharper edges of the abrading grits are presented at the abrading surface.

It is also contemplated as an object of my invention to provide an adjustment of the constituents of the waterproong materials and volatile vehicle used therefor comprising, generally, resinous and oily constituents whereby the various steps of application of the coats comprising the presize for the backing, the binder coat for the grit, the backsize and the sand-size, will permit the sheet carrying these coatings to pass through the drying and heat-treating steps with great speed and facility so that the coatings quickly take on suiiicient rigidity whereby the sheet may be handled without external mechanical pressure which would otherwise be necessary Ato render the constituents of the binder homo.-

genous and, which if applied, would disturb the abrasive particles and present a duller working abrading surface.

A still further object of my invention resides in the provision of waterproofing compositions, serving as sizing or binder coats in the production. of waterproof and exible sandpaper of value in the practice 0f the methods hereinbefore referred to, assuring the economical and uniform production of waterproof and flexible sandpaper of the maximum abrading efliciency.

For the attainment of the aforementioned objects and for such lother objects as may appear herein or may be hereinafter pointed out, and

for a clearer understanding of the method contemplated by my invention, reference will now be made to the accompanying drawing forming a part hereof, in which the Figures 1 and la. are

diagrammatic illustrations of the sandpaper making process in accordance with my invention.

In this View, a backing material I is provided in the form of a continuous sheet and is fed to printing rolls H for the proper identification of the sandpaper to indicatev the grade of paper or for the application of a trade mark and similar notations. From the printing roll, the backing is then fed to pressure transfer rolls I2 whereby a presize is afxed to one surface of the pa}er.

permitted to fall freely from the surface of the web. The fabric carrying the sizing coat, binder coat and abrasive is then passed over a festooning rack II after which the web is passed through an oven I8 having suitable festooning racks.

I nd it desirable that the sheet or backingl material I0, after receiving the grit layer from the hopper I and while passed through the festooning steps indicated at I1 and through the oven, as indicated at I8, to so conduct the backing that the grit coated side thereof is maintained out of direct contact with pressure rolls so that from the time of application of the grit until the adhesive is substantially fully set, passing from the chamber of the oven IB, the grits do not become dulled or materially disturbed and thus, when the finished article is rolled upon the making roll 2|, the adhesive is sufliciently set so as to prevent turning over the grits from a predetermined deposited position so that a relatively large number of the grits will be presented with their sharper cutting edges outwardlys Where the paper is carried through the secondary step of the operation, as hereinafter described, I also, in this instance, maintain the sheet out of contact with the pressure rolls, with the exception of the point atwhich the sand sizing coat may be applied if desired.

I find that I am ablev to avoid direct contact with pressure rolls which may disturb the desirable position of the abasive particles, by reason of the character and nature of the waterproofing compositionthat I use and which will be more particularly referred to hereinafter, constituting the copolymerized and reaction product of resinous materials, 'particularly a phenol-fatty-oil-reactive resin and a fatty oil" in a volatile vehicle. The homogeneity of this product andthe speed with which it sets and matures enables me to handle the web in the manner hereinbefore decribed. The oven is divided into chambers I9 and 20, respectively, the first of which is heated at a relatively high temperature, and the second of which maintains a temperature materially lower than the first chamber. Up to this point, the webbing may be said to have been going Jthrough the making process, and may thereafter be formed into a roll 2l to await treatment for finishing by sizing.

However, the making process may be followed immediately by the sizing in a continuous operation, and for this purpose, the web may then be passed through pressure transfer rolls 22, where a i'llm of back-size is applied to the surface of the webbing opposite to that carrying the abrasivev particles.- The webbing thus treated may then be passed through festooning racks 23, and then immediately passed through pressure transfer rolls 24, where a film of a sandsizing is applied to the grit surface of the web so prepared. The web then passes through ovens 25 and 26 respectively, the first of which is maintained at a higher temperature, the second of which is maintained at' a relatively lower temperature. In these ovens, as well as the ovens previously mentioned at I8 and 20, means are provided to control the humidity within the-ovens to about 38%.

From the oven 26, the composite sheet so pre- Pared is rst subjected to a mist of water by the spraying device 28 sprayed on the back-size in quantities just sufficient, so that the paper does not cockle, from which point; the composite is then formed into a roll 29 to await suitable treatment subsequently by cutting the same into small sheets, disks, rolls or other forms for the market.

For the continuous operation briey above referred to, in connection with the diagrammatic illustration of the process, to attain the objectives heretofore mentioned, reference will now be made .to the details of the process briefly described above.

The success of the process involves a proper relationship of the backing material to the size in order to afford a proper preliminary preparation of the paper for the subsequent treatment, and to permit of a continuous operation which will produce uniformity of results. The paper webbing, where lthis form of backing material is used, is so chosen, as well as the consistency of the sizing composition and method of applying it, to assure a continuous film upon the backing rof minimum penetration, yet of denite uniformity.

For this purpose, with a sizing material of the character .to be described and the method of application to .be described, I provide a paper stock which has an oil absorption factor of thirtyve minutes, made by the Fourdrinier method.

The sizing composition and the method of applying it are so controlled as to give a continuous film of about six to .l2 grains per square foot, and for this purpose, pressure rolls whereby the uid sizing coat has transferred to it the sizing material, above referred to. y

In my preferred form of the invention, a sizing coat of the following formula is used:

are utilized at the point I2 l This formula in relation to the paper backing ofthe character above referred to, is most suitable for my purposes. The paper should be a hard, tinny sheet without shiny spots and as free as possible from such defects as slime spots, dark spots, wrinkles and cockels. Thel utilization of a sizing coating of the character described, is charavoiding undue penetration of the extremely thin film of sizing material, so that a continuous fllm is provided, cooperating with the backing to provide an extremely flexible product.

Following the application of asizing coat, the web passes over the festooning racks I3 so as I to evaporate by aeration, the solvent of the sizing coat. vThe surface exposure of the festooning Y racks is such that'withina period of about thirtyfive minutes, the web has completely passes over the racks, and the presize coat is now in condition for having applied thereto the bindercoat.

to the solvents which characterizes the formulas above enumerated as B and `C constitutingV the essential features of my invention, particularly in relation to the abrasiveparticles and to the sizing material initially deposited upon the backing, vis the,l ability of the thinner vto maintain the ingredients in perfect solution at all times` up to .the end point of evaporation, notwithstanding the wetting elect the bin-der may have upon the grit or abrasive particles, or the capillary attraction caused by contacting particles of grit. The binder coat in relation to thesizing coat is `further characterized by anchorage to the sizing coat without `re-solution to an extent as will causeY penetration of the sizing coat" into the backing material with the consequent starving of the binder coat. i

For grits of a fineness 'of from 220 to 400 mesh, I may increase the fluidity of the binder coat by the addition of a greater amount of thinners in percentage of about 15% for 220 mesh and 25% for 400 mesh. At all times, this percentage and the character of thinners used is such that the oils and resins and soluble materials, where organic drier-s are used, are such that the materials ,y will be kept in solution Without segregation and In accordance with "the apparatus heretofore f described, the binder coat isapplied by pressure i rolls I4, one of the rollsof the series being dipped 35 into .a tank including the binder composition,

l For grits of a mesh of 60 to 120, the following binder coat compositions may be used:

Immediately followingsthe application of the binder coat by the method described, the abrasive particles are sprinkled over the binder'coat,-pref erably heating .the grit to a temperature of about 1GO degrees F.

Vto the end point of evaporation of the thinners, even where baking temperatures are Aused to evaporate the thinners. The mixed thinners used are further characterized by the fact that the entire solution wets the abrasive, and under the influence of the wettingv action of the abrasive particles,`the mixed thinners which are used are characterized by complete solution of the organic materials used in the thinners up to the end point of evaporation.

It will further be observed that the character of binder coat used in relation to the sizing coat and the treatment given tothe sizing coat will result in a predetermined -thickness or depth of film being formed upon the sizing coat to leave a film of binder which anchors the lgrit to a predetermined depth 'and to properly expose the abrading edges. 'I'his relationship of the binder coat to the sizing coat is particularly important with the finer mesh grits, to assure proper abrading efficiency with adequate anchoring of these particles.

Following the application of the binder coat and grit, the webbing carrying the materials are festooned as described over the festooning Y racks I'I for a short period to initially -remove Example B Per cent China-wood oil 24.4 Rosin' 4.0'7 Lime .13 Manganese oxide .29 Litharge .O8 Kauri 12.2 Ester gum 6.5 Linseed oil (boiled) 2'7.53 oleum spirits 10.5 Wood turpentine 14.3-

Earample C China-wood oil 60.0 Phenol formaldehyde resin 19.8 60 Linseed oil .13 Rosin, .006 Lime .001 Litharge .002

Cobalt acetate .001l Turpentine 19.93 Oleum spirits .13 Manganese oxide Trace 'Ihe relationship of the mixed resins and gums 15 some of the thinners. The web then passes into the oven I8 at the compartment I9 over racks included therein in number suiiicient to pass through the compartment I9 within a period of two hours. The compartment I 9 is maintained at a temperature of about 175 degrees F., provi sion being made todraw off such volatile vapors as may be generated by reason of thethinners that are used.

The passage of the web through the compartment I9 is for such period of time so that at faces maintained within the compartment 20 is such aswto prolong this compartment for a period of about twenty-eight hours. At the end of this period of time, the binder has been thoroughly matured and as previously described', the web may be formed into the roll 2l to'be stored `for subsequent use in the sizing operations.'

The web, however, may be fed continuously to the applicator 22 which includes pressure tra-nsfer rolls, at which point a composition as follows may be applied to the back of the .web as a backsize, the composition being as follows:

The composition under Example D is maintained at a temperature of.V about 130 degrees F.

'I'his formula under the method of application is characterized by sufficient fluidity to form a continuous lm by its further property of being anchored to the backing material at the back surface without impregnation to any extent as would alter. the first sizing coat by striking through to the front face of the backing. The formula andthe method of application are further characterized by compatability with the backing, to result in a film which will resist decomposition by the liquids used in abrading operations, yet offering suicient frictional characteristics at the back surface. l A

After application of the formula in accordance with Example D, the webbing is air-dried by passing the web over festooning racks 23 for a period of about thirty-five minutes. The web then passes through the applicator in the nature of pressure transfer rolls 26, at which point the sandsize is applied to the grit surface.

At this point, a composition in the nature of following is applied:

Example E p Per cent China wood oil; 35.2 Rosin 5.41 Ester gum l 7.11 Lime 0.18 Manganese oxide 0.05 Litharge 0.10 Y Lead acetate- 0.03 Turpentine 6.67 Oleum spirits 45.25

However, I may use, for thel sandsize, a composition as follows: A

Example F u China wood oil 37.5 Phenel formaldehyde resin (oil reactive The sand size is maintained at a temperature of about 100 degrees F. during this application. The webbing is then passed through successive compartments 25 and '26 and an oven at temperatures of about 175 degrees F., 140 degrees F. in the respective ovens 25 and' 26.

The relationship of the thinners to the binding materials, suchas the oils landresins in the backsize and s'andsize, is such as to minimize solvent action upon the underlying coat in the case of the sandsize, to avoid any softening or swelling of the binder coat. vAt the Sametime these materials should,be of suiiicient fluidity to seal up am; pores which may have been caused by the evaporation of 'the solvent in the binder coat, or b'y the baking treatment to which the binder coat has been subjected.

The relationship of the ingredients to the thinner is further characterized b'y the ability of the thinner to maintain the solids substantially in perfect solution up to the end point of the evaporation o f the thinners, to resultin a film having the composite characteristics of all the residual ingredients uniformly blended'.

Following the baking operation in the chambers 25 and 26, andbefore winding the composite article into rolls, the back surface of the webbing is sprayed. with a mist of water in quantities just sufficient so that the paper does ,not cockie, the paper therefore being iexibilized by the' moisture that is absorbed. The Vcomposite may then be formed into rolls and is then ready- \to be cut up into the nal marketable article.

resin) 12.35 Linseed oi1 .08 Resin -.004l Lime Trace Litharge .001 Cobalt acetate .001 y, Turpentine 50.0

f Manganese oxide Trace stituents and fatty I have herenbefore given specificy examples of formulae which I prefer for purposes of making. a sizing coat. binder coat, back-size or sandsize. In general, the proportions given may be varied and still obtain a high order of desirable results.

gradients may be varied within limits more particularly set forth inthe .co-pending application of Carlton and 0akes,}"` entitled Waterproof sandpaper and the method of making the'same, filed on equal date with thisapplicationserlai No. 660,319.v Accordinghn', lthe"reainouscon'- cils-.may befvari'ed within the following limits: f'

Resinous materials l2 to 39%; fatty 'oils from 8l to 50%; driers from .5 to 1%, and the balance up to about 49% of-volatile thinners, the volatile thinners being variable, determined vupon the point at which the composition is to bensed,r

either as apaper sizing coat, binder coat, backsize or sand-size, further taking into account the nature of the backing material 'to be treated, the thickness of the binder coat that is desired, the size and nature of the abrasive particles.

In formulae C and F, `I have referred toa phenol formaldehyde resin. specifying an oilreactive resin. Where the oil-reactive resin is used, it is preferred by me to use'the oil reactive .resin described in the aforementioned Carlton- Oakes application, and comprising a "phenol-fatty-oiI-reactive resin, and where this form of oil reactive resin is used, it is submitted to polymerization in conjunction with a quality or the full amount of fatty oil designated in the various `formulae. This combination of constituents is preferred by me as most suitable for practicing the process of making sandpaper in accordance with my invention hereinbefore described, in that the co-polymerization of the phenol-fatty-ollreactive resin and the quantity of fatty oil designated lends itself peculiarly desirable to making sandpaper in accordance with my process in' that The essential ingredients are the resinous components and fattyoilsand these inf .it permits a continuity of steps beginning with thev application of the pre-size, followed by the application of'the binder and, if desired, after application of the abrasive particles, the web vcarrying these layers may passin a shortftime,

directly and in ya continuous operation, vto the point where the back-size" is' applied and then l' to the point ywhere the sandsize is applied.

4Where I use the polymerization' reaction product of a phenol-fatty-oil-reactive resinfand the fatty'oil in the volatile solvents,`the'web may anced compositel waterproofing lmaterial or binder in theclaims, I meansto lincludewithin the `scope thereof a binder havingfcharacteristics labove mentionedspecifically in this paragraph.

I also consider'as novel lin'iny invention the application of Ithe 'grit/'in vthe manner set out yand the removal of excess' grit,"together with the heating steps1v and subsequentltreatment by "sizing coatslwherein the gritcoatedside'of the sheet is ,maintained free of eXternalDreSsure,

- thus preventing dulling of 'the yfinished Iarticle.

pass through the pre-sizing operation and then j to the point where the binder coat is Vapplied with maximum speed, as only 'suicient time necessary forvolatilization Vrof a portion of the -I also attribute the attainment of the novel uffeatures `above""described, permittingfth' -consolvent and aeration of the coating need `v expire 4' i and suicient body will be given to the pre-sizing coat to permit 'it to directly `pass to the point 'It will befobserved that from the disclosure l made,'I have provided compositions of particular utility inl making. waterproofl sandpaper" and a i method for preparing 'waterproofl sandpaper,

having all Athe inherent advantages and desirable properties heretofore emphasized andv which may `serve to attain proper anchorage of the -abrasive particles for `maximum abrading eficiency, and uniformity ofthe en d product and I consider the scope of my invention as pertaining tothe compositions as residing in the provision of a composition particularly suitable for surface coating of the backing material used in making the sandpaper or-the backing material having superimposed thereon a grit or layer of abrasive particles in which a proper balance of the vehicle is used, together with the resinous materials, in which the volatile components are so balanced that perfect solution of the waterproofing materials are maintained to the end point tinuity of operations, tothe natureand character ofthe rsinou's and oily constituents in the volatile vehicle, these materials being balanced y'in perfectsolution up to themen'dpoint of evaperation of the volatile vehicle, especiallyin the presence of lthe' grit'or layer of abrasive `parti cles, and external pressure necessary for handling or Vuniting the coatings fand which .would otherwise disturbthe efficiency of th'e' abrading characteristics of thel particles,` is avoided.

AI furtherA consider that the' novel characteristics of the `method"herein described/for the formation ofthe waterproofing sandpaperI resides in the control of the ternperature andv speed of volatilization of the volatile thinner'or solvents, and that this includes the control of the temjperatureand the speed of volatilizationabove the dew'point of the atmosphere in'which the volatilization" of the thinner is conductedand `that this model of operation materially contributes to the `production of an abrasive product of evaporation, in the presence of porous solid materials, such as the backing, of in th'e presence of solid materials, such asthe abrasive particles which are used. And I consider my invention to reside in the application of waterproofing materials to a backing material, or as a binder for an abrasive sheet or a size therefor, in which the inherent characteristics of the waterproofing materials in connection with the volatile solvent or a diluent are so balanced as to be characterized by perfect solution to the end point of evaporation, particularly in the presence of solid materials, or porous solid ma.- terials constituting either the backing material or `the grit or layer of abrasive particles. And I further consider that the compositions herein disclosed and the method of producing the having high abrading efficiency and uniformity.

Having thus described my invention and illustrated its use, what I claimv as new and desire to secure by Letters Patent, is:

l. The method of forming an abrasive article including the steps of applying to a backing ma; terial a sizing coating of a balanced composite" waterproofing material of a polymerized resinoil complex homogeneously distributed ina volatile vehicle, aerating thebacking so treated to remove a portion of the volatile vehicle and oxidizing the sizing coat, applying a balanced composite waterproofing binder coating thereover comprising a resin-oil complex homogeneously, distributed in the volatile vehicle, depositing a grit or layer of abrasive particles, diverting the abrasive particles from the binder coating in a direction away from the adhesive for removing the excess of the abrasive particlesand then aerating to remove the volatile vehicle to the end point of evaporation ofthe volatile vehicle, oxidizing the residuum in the presence of heat, the web being passed through the aeration and` oxidizing steps under conditions leaving the abwaterproof sandpaper herein described is characterized by the blend of the materials constituting the waterproofing material and the vehicle which, in the form of the final product, will result in an .abrasive article of high efliciency, and with uniformity of characteristics, in that the waterproofing material will not flow from the grit Aor abrasive particles under the process of producing the nal article, or cause any .undue creeping of the binder in relationto the grit, in nally forming the article all of which characteristics hereinabove ascribed to my preferred form of binder which, for convenience, I term as balanced composite waterproofing rasive surface exposed and free from external pressure. until the coatings applied are set.

2. The method of forming an abrasive article including the steps of applying a rapidly setting sizing adhesive comprising a polymerized material or binder. Where I use the term balresin-oil complex to one side of a backing material, conducting the backing so as to aerate the sizing adliesive,` then immediately applying an adhesive formed of a balanced composite waterproong material comprising a polymerized oil-resin complex in plastic state to the sized surface of said'backing and while said adhesive is still plastic applying a grit or layer of abrasive particles upon the adhesive coated side of said backing, and diverting the abrasive from the adhesive coated side in a direction away from the adhesive for removing the excess of of abrasive particles Without external pressure upon thel abrasive i coated surfaceV from the point of deposition of -grituntil the adhesive is set.

' 3. The methodof forming an abrasive article including the steps of applying a rapidly setting sizing adhesive comprising a polymerized resinfatty-oil complextoue side of a backingmaterial, conducting the backing `so as to aerate the sizing adhesive, then immediately applying an adhesive formed of a balanced composite face from the point of deposition of the grit until the adhesive isset.

' said particles; then continuously feeding the backing so prepared and subjecting same to heat reactive resin and a fatty oil in a volatile vehicle, depositing a grit or layer of abrasive particles, aerating the backing material and its coatings to separate a portion of the volatile vehicle by disposing theweb to expose the surface coating thereof without .external pressure, oxidizing the last mentioned coating in the presence of heat whileoxidizingthe surface thereof without external pressure upon the abrasive coated surface from the point of deposition of the grit or layer of abrasive particles until the binder coat is set. y

6. In the method of forming anabrasive article in the natureof sandpaper, the steps which `include continuously and progressively applying.

successive coats formed of a balanced compositef' waterproofing material to one side of a backing material in successive coatings, said material being formed o1' a polymerized resinfatty oil complex homogeneously distributed in A a volatile vehicle, each of the successive coats 4. The method of forming an abrasive article including the steps of continuously and progressively applying to a carrier successive coats formed of a balanced composite waterproong material of a polymerized phenol-fatty-oil-relactive resin and fatty oil in a volatile vehicle,

each of the successive coats being subjected to aeration and oxidation during intervals between the application of the coats, one of said coatings being followed by a deposition of a grit or Alayer while the coating is in a plastic state. Y

, 5. In the method of forming an abrasive article, thesteps which include applying a sizing coat to a backing material comprising a polymerized reaction product of a oil-reactive resin vehicle, aerating the coating so deposited upon the backing, overlying a balanced composite waterproofing binder coat comprising a polymerized reaction product of a phenol-fatty-oilfphenol-fattybeing subjected to' aeration and oxidation during the application ofthe coats, the period of operation for the rst of said coats partially setting the polymerized fatty oil resin complex, one of said coatings being followed by a deposition of the grit or layer of abrasive particles while the coating is in a plastic state.

7. In the method of forming an abrasive article in the nature of sandpaper, the steps which include continuously and progressively applying successive coats formed of a balanced compcsite waterprooiing material to one side of a backing material in successive coatings, said material being -formed of a polymerized phenol- A fatty-oil-reactive-resin and a fatty oillhomoand a fattyfoil in a volatile geneously distributed in a volatile vehicle, each of the successive coats being subjected to aeration and oxidation during intervals between the application of the coats, the period of operation for the iirst of said coats partially setting the said polymerized resin land oil, o ne of said coatings being followed by a deposition of' the grit or layer of abrasive particles whilethe coating is in a plastic state.

. BYRON J. OAKES. 

